Tetrachloroethylene stabilized by 2-halothiophene



iatented Dec. 9,

TETRACHLOROETHYLENE STABILIZED BY Z-HALOTHIOEHENE Robert S. Cooper,Painesville, Ohio, assignor to Diamond Alkali Company, Cleveland, Ohio,a

corporation of Delaware No Drawing. Application May 18, 1959, Serial'No.162,820

3 Claims.

This invention relates to inhibiting the decomposition oftetrachloroethylene catalyzed by light, air, heat, moisture, and metalsurfaces and more particularly relates to a composition of matterconsisting essentially of tetrachloroethylene and stabilizing amounts ofa compound of the group of 2-chlorothiophene and Z-bromothiophene.

It has heretofore been known that tetrachloroethylene(perchloroethylene) of a high degree of purity and containing onlyminute amounts of saturated, or other unsaturated, lower aliphaticchloro-hydrocarbons is very inert to the action of air, light, heat,moisture, and metal surfaces with which it comes into contact duringstorage and commercial use. However, the obtaining of such high puritytetrachloroethylene in commercial production is not generally feasibleand it has been found that the impure material normally encountered incommerce decomposes when in contact with the substances noted above.Hence, means other than purification for preventing or inhibiting thedecomposition of tetrachloroethylene and the lower chlorinated aliphatichydrocarbons generally associated therewith must be had.

It is generally believed that tetrachloroethylene exposed to air, light,heat, moisture, etc., decomposes, especially in the presence ofmoisture, principally by way of oxidative attack at the double bondinvolving a series of steps in which the ultimate products includephosgene, trichloroacetic acid, and hydrogen chloride. It is alsobelieved that the oxidative attack is catalyzed by light and by theproducts of oxidation, as a result of which, oxidative decompositiononce initiated is self-catalyzing and self-sustaining. Otherchloro-hydrocarbons generally associated with crude commercialtetrachloroethylene also are subject to oxidative attack and decomposeto some of the same products as those formed by the oxidation oftetrachloroethylene, and at a somewhat accelerated rate, as compared tothe oxidation of tetrachloroethylene. These products are then availableto catalyze the decomposition of the tetrachloroethylene. For example,tetrachloroethylene obtained commercially from the crude products ofchlorination and chlorinolysis of lower aliphatic hydrocarbons maycontain small but appreciable amounts of saturated and unsaturatedchlorinated hydrocarbons, such as dichloroethylene, trichloroethylene,trichloroethane, unsymmetrical tetrachloroethane, pentachloroethane, andthe like. These lower chloro-hydrocarbons in themselves are relativelyinnocuous in solvent extraction processes in which thetetrachloroethylene is used, but the oxidation decomposition productsthereof corrode metal surfaces with which a body ofvtetrachloroethylenecontaining them comes into contact. These less stablechloro-hydrocarbons are believed to be the principal initial sourc ofchloro-oxygen-containing impurities, such as phosgene, ch-loroaceticacid, trichloroacetic acid, and the like, in the tetrachloroethylene,which impurities catalyze decomposition of the tetrachloroethylene.

Ihe problem, therefore, is principally one of inhibiting the initiationof the oxidation of the chlorohydrocarbons commonly associated withcommercial tetrachloroethylene, as well as inhibfiting the oxidation oftetrachloroethylene itse One of the objects of the present invention isto provide means for inhibiting oxidation of tetrachloroethylene andlower aliphatic chlorohydrocarbons generally associated therewith duringexposure to air, light, heat, moisture, and metal surfaces.

Another object of the invention is to provide a procedure for treatingand purifying crude tetrachloroethylene in order to obtain maximumefficiency of the stabilizer in the purified product.

These and other objects will be apparent to those skilled in the artfrom the discussion hereinafter.

It has now been found that where the crude tetrachloroethylene,particularly that obtained from commercial processes involving thechlorinolysis of lower hydrocarbons or hydrocarbon chlorides, or thechlorination and simultaneous dehydrochlorination of hydrocarbonchlorides, such as ethylene dichloride, or of unsaturated hydrocarbons,such as acetylene, ethylene, eth-- ane, and the like,contains'appreciable amounts of lower chlorinated aliphatic hydrocarbonsother than tetrachloroethylene as impurities, such crude product mayinitially be treated with an aqueous solution of an inorganic base and ahigh boiling point organic base in order to destroy the major portion ofvolatile acids and acidforming impurities, and then combined with 2-chlorothiophene or Z-bromothiophene, whereby decomposition of thetetrachloroethylene and other lower chlorinated aliphatic hydrocarbonsis inhibited underthe most adverseconditions. of storage and commercialuse. In general, the present invention is directed to. a compositionstabilizing amounts of a compound ofthe genoral-formula contaminatedwith minor amounts of other lower aliphatic chloro-hydrocarbons, both inthe liquid and in the vapor phase. For the most part, the stabilizingeffect has been found to be most pronounced and prolonged wherepretreatments which destroy the greater part of the chloro-acids andacid chlorides have been resorted to prior to combining thetetrachloroethylene with Z-chlorothiophene or 2-bromothiophene.

The initial treatment of the crude tetrachloroethylene may includeadding an organic base of the amine type and having a boiling pointhigher than tetrachloroethylene, for example, aniline or morpholine, inan amount from approximately 0.2-2.0% by weight to the crude product,and fractionally distilling the crude mass to recover substantially allof the tetrachloroethylene as an intermediate fraction in thedistillation; additional treatments may include washin thetetrachloroethylene fraction with a solution of an inorganic base, suchas an alkali metal or alkaline earth metal base, for example, sodiumhydroxide, sodium carbonate, calcium hydroxide, magnesium bicarbonate,and the like, drying the washed product and distilling the dried productto recover a more highly refined tetrachloroethylene fraction. Thepurpose in using an amine, such as aniline, is to allow for the reactionof such amine with acid chloride products contained in the crudeproduct, whereby an anilide or analogous compound may form duringdistillation and the undesired impurity is retained in the distillationresidue. The purpose of washing the efiluent from the initialdistillation with an alkali metal or alkaline earth metal base is toremove the more volatile of the acid chloride impurities, such ashydrogen chloride, phosgene, and the like, which may not have reactedwith the amine.

The crude product may also be washed initially with a solution of aninorganic base, such as those noted aboVe, dried, and combined with anamine having a boiling point substantially higher thantetrachloroethylene, generally in an amount from 0.2-2.0% by weight, andthe mixture thus obtained distilled as described above in order torecover the purified tetrachloroethylene substantially free fromchloro-oxygen-containing impurities.

Where such impurities as hydrogen chloride, phosgene, chloro-acids, andthe like, are known to be extremely low in the crude product, thismaterial may be combined with an amine, such as aniline, as notedhereinabove, and subjected to fractional distillation to recover thesubstantially pure tetrachloroethylene without the necessity ofresorting to the treatment With a solution of an inorganic base.Moreover, the dilute alkaline wash may be omitted even where thechloro-oxygen-containing compounds are present in appreciable quantitiesin the crude product, but it has been found that the amount of organicamine consumed and the volume of distillation residue accumulated areexcessive.

After any one of the above-described initial treatments, the recoveredtetrachloroethylene may be combined with a stabilizing amount of2-chlorothiophene or 2-bromothiophene, noted above, for example, in anamount from 0.0l 1.0% by weight of tetrachloroethylene, preferably,however, from 02-03% where the above pretreatments or their equivalenthave been used. The extremes within the above-noted broad range arepreferred where the amount of chlorohydrocarbon impurities associatedwith the tetrachloroethylene is unusually high or unusually low, whilethe amounts within the intermediate preferred range are generallysufficiently effective where the purified tetrachloroethylene containsnot more than about 1-3% of the lower chlorinated aliphatic hydrocarbonimpurities consisting essentially of trichloroethylene, the most commonimpurity obtained in commercial production.

The beneficial effects of the present invention may also be realizedwhere tetrachloroethylene has been purified in a commercial operationand stabilized either with a high boiling point stabilizer,. i. e., astabilizer such as one of the amine or of the ether type having a higherboiling point than that of tetrachloroethylene, or with stabilizerswhich are more volatile than tetrachloroethylene, by removing suchstabilizer as by chemical reaction, azeotropic distillation, or thelike; the thus-treated mass is then fractionally distilled to recoverthe tetrachloroethylene fraction, which may be combined with a member ofthe group of 2-chlorothiophene and 2-bromothiophene, noted hereinabove,in an amount suificient to efiect stabilization, whereby thtetrachloroethylene is rendered especially suitable, due to itsstability, for degreasing or dry cleaning operations.

In order that those skilled in the art may better understand the presentinvention and in what manner the same may be carried into effect, thefollowing specific examples are offered:

Example 1 Crude tetrachloroethylene obtained from the distillation unitof a commercial tetrachloroethylene plant is washed with a dilutesolution of soda ash (10%), dried over anhydrous calcium chloride, andcombined with 0.25% by Weight of aniline, and the material subjected tofractional distillation. The fraction boiling between 120.5 and 121.5 C.is taken for a stability test. Two 25-ml. samples of thetetrachloroethylene are placed in round-bottom, oneneck flasks and toone of these samples there is added 0.25% by weight ofZ-chlorothiophene. To each of the flasks there is added an amount ofwater equal to 2% by weight of the tetrachloroethylene and a weighedstrip of aluminum foil; the contents of the flasks are subjected toreflux for a period of 24 hours. Thereafter, the tetrachloroethylene isextracted with distilled water, the extract analyzed for chloride ion(titration with 0.02N AgNOz) according to the Volhard method and thealuminum strips Washed, dried and reweighed, with the following results:

- Gms. Cl Liter Sample i gzl'g Tetrach loroethylene R Containing 2Chlorothio- Less than] mg... Trace.

p ene. Control d0 0.006.

Example II from l20.2 C. to l21.7 C. is taken as the tetrachloroethylenecut. Two 25-ml. portions of this tetrachloroethylene out are placed inroundbottom flasks and a strip of aluminum foil is added thereto. To oneof the flasks is added 2-chlorothiophene in an amount of 0.25% by weightof the tetrachloroethylene contained therein, and to both of the flasksthere is added 0.8 ml. of water. The flasks and contents are heated tothe reflux temperature for tetrachloroethylene for a period of 24 hours,cooled, extracted with distilled water and the aluminum strips washed,dried and weighed, as in Example I, with the following results:

- Gms. (ll/Liter Loss in Weight Sample Tetrachlorc- A1 Smp ethyleneContaining 2 Chlorothio- Less than 1 mg 0. 004

phene. Control do 0. 010

Example III A batch of crude chloro-hydrccarbons from a commercial unitproducing tetrachloroethylene and trichloroethylene is initially treatedto remove saturated chlorohydrocarbons and chlorooxygen-containingcompounds and subsequently fractionated to separate thetetrachloroethylene from the other chloro-hydrocarbons. Two 25-ml.portions of this tetrachloroethylene fraction are placed in round-bottomflasks and to one of the portions there is added 0.25% by weight of 2-chlorothiophene and to each of the flasks there 3 is added 0.8 ml. ofwater and a weighed strip of aluminum foil. The contents of the flaskare refluxed for a period of 24 hours, cooled, extracted with distilledwater, and the strips of aluminum foil washed, dried and weighed, as inExample I, with the following results:

Gms. Cl/Liter Loss in Weight Sam le Tetrachlorop A1 Sm? ethyleneContaining 2 Ohlorothio- Less than 1 mg 0. 001

phene.

Control -do 0. 049

Example IV 'B. 25-m1. portions of these two samples are subjected to thestability tests described in Example I above, with the followingresults:

- Gms'. Cl/Liter Gain 0r Loss in Sam le Tetrachlorop Weight of Al Stripethylene Containing 2 Chlorotbio- Less than 1 mg... 0.001

phone "A". Control-"A" .do O. 009 Containing 2 Ohlorothio- ..-..do 0.004

phene B". Control-"B" -.(lo 0. 007

Emmple V Boiling Fraction No. Point, C.

' Grns. Gl/Liter Loss in Weight Sample Tetrachloroof Al Strip ethylene(1) 2-Bromothiophene Less than 1 mg Trace (2) 2Bromothiophene.. ontr (3)2-Bromothiophene While there have been described various embodiments ofthe invention, the products described are not intended to be understoodas limiting the scope of the invention as it is realized that changestherewithin are possible and it is further intended that each elementrecited in any of the following claims is to be understood as referringto all equivalent elements for accomplishing substantially the sameresults in substantially the same or equivalent manner, it beingintended to cover the invention broadly in whatever form its principlemay be utilized.

What is claimed is:

l. A composition of matter consisting essentially of tetrachloroethyleneand a stabilizing amount of a compound chosen from the group consistingof 2-chlorothiophene and 2-bromothiophene.

2. A composition of matter consisting essentially of tetrachloroethyleneand a stabilizing amount of 2-0hlorothiophene.

3. A composition of matter consisting essentially of tetrachloroethyleneand a stabilizing amount of 2-bromothiophene.

ROBERT S. COOPER.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,917,073 Stewart et a1. July 4,1933 2,440,100 Klabunde Apr. 20, 1948

1. A COMPOSITION OF MATTER CONSISTING ESSENTIALLY OF TETRACHLOROETHYLENEAND A STABILIZING AMOUNT OF A COMPOUND CHOSEN FROM THE GROUP CONSISTINGOF 2-CHLOROTHIOPHENE AND 2-BROMOTHIOPHENE.